More animations for custom mobs?

I was wondering if we could ever get more animations to choose from when adding a new entity model, for example, spider leg animations, I was making a new spiders mod and wanted to make changes to the models but if I made a custom model then I wouldn't have the animations for the spider.

Or another example, say I'm trying to make a blaze with a custom model, I can't make the rods move around it and look good.

That's all I really have to say. Thank you for reading.